class AbstractModeHandler:
    def __init__(self, event_handler, diagram, gui):
        self._event_handler = event_handler
        self._diagram = diagram
        self._gui = gui
    def key_pressed(self, event):
        pass
    def button_pressed(self, event):
        pass
    def button_released(self):
        pass
    def mouse_moved(self):
        pass
